Monday, January 19, 2009

PARIS (AFP) If you could put an animal in a time machine and send it back to live in the distant past, would its DNA evolve in reverse, returning to the genetic code of its ancestors?

The intriguing idea has been tested by scientists in Portugal and the United States, using the fruit fly (Drosophila melanogaster) as the animal, and a laboratory to recreate the conditions of the past.

The modern-day fruit flies were the distant descendants of an original group that had been harvested in the wild back in 1975.

Over the following decades, 500 generations of flies grew up in different environments.

Different groups of insects were starved, exposed to greater humidity and so on in various research projects, and as a result developed specific characteristics, moulded by these conditions.

Henrique Teotonio and colleagues put these various populations back into the ancestral environment and let them reproduce for another 50 generations.

They then took a close look at a telltale stretch of DNA, on Chromosome 3, to see whether "reverse evolution" had taken place.

The answer: Yes, it had, but only up to a point.

Once the flies had adapted comfortably to their new environment, the backwards-winding clock of evolution came to a halt, according to their paper, published on Sunday in the journal Nature Genetics.

"Reverse evolution seems to stop when the populations of flies achieve adaptation to the ancestral environment, which may not coincide with the ancestral [genetic] state," said Teotonio.

"On average, only half of the gene frequencies revert to the ancestral gene frequencies. Evolution is contingent upon history at the genetic level, too."

The work also suggests evolution is rather more complex and less linear than is generally thought, Teotonio said.

For one thing, it shows that species can evolve from generation to generation by reshuffling variant forms of a gene, rather than introducing new mutations of it, he said.from: http://news.yahoo.com/s/afp/20090111/sc_afp/scienceevolution_newsmlmmd;_ylt=Aiwl1M2lY3WVSPGLuYv4XojPOrgF